1. Field of the Invention
The invention relates to an erasing and cleaning device for the cleaning of cylindrical surfaces, in particular the surfaces of printing-forme and rubber-blanket cylinders inside and outside of printing machines, with the aid of a cleaning cloth capable of being guided by cleaning-cloth transport means.
2. Description of the Related Art
In the field of printing technology, as is known, in the devices often used for cleaning cylindrical surfaces a cloth is guided past the surface of a rotating cylindrical object, and this cloth, impregnated with cleaning agent, takes up the dissolved-on and dissolved substances from the printing forme and transports them away. The cloth is unwound from a fresh-cloth roll and, after use, is wound up on a dirty-cloth roll.
A cleaning system for printing formes is known, for example, from the publication DE 44 42 412 A1, which discloses a method and a device for controlling the washing mode in a printing machine. The object to be achieved in that publication is based on the recognition that the feed for the cleaning cloth must be controlled more accurately, more reliably and in a more versatile way. This object is achieved, in that publication, essentially in that the cleaning-cloth transport receives via a sensor, from a clocked gearwheel, travel-proportional pulses which are used to control the drive motors for the transport means of the cleaning cloth, so that the respective transport travels of the cleaning cloth can be kept constant.
In order to achieve defined transport travels, the transport travel of the cleaning cloth in the forward and backward directions is detected by a tracer means having a rubber wheel rolling on the cleaning cloth. An exchangeable so-called push-in washing unit has a tracer means in the form of a clocking shaft, on which the cleaning cloth rolls, and a sensor which is fastened to the printing machine and which senses a toothed clocking wheel connected to the clocking shaft, the thickness of the clean-cloth roll also being sensed by a resiliently pressed-on tag which cooperates mechanically with a second machine-side sensor.
With the push-in washing unit inserted, the drums can be driven by a single motor which is arranged on the printing machine and, depending on the direction of rotation of said motor, rotates either one drum or the other, as is known per se from EP 0 520 521 A1.
A measure, which is simple to form, for the transport speed of the cleaning cloth is the frequency of signals obtained from regular markings which are formed on the tracer means.
The above-mentioned known arrangement requires a separate control mechanism which necessitates an outlay in terms of material and of maintenance.
EP 0 693 371 B1 describes a forme cylinder which has an anodized or brushed seamless aluminium or chromium surface. It is imaged by the thermotransfer method. Provided on the circumference is a device which serves for removing the printing image after the printing process has ended.
After the printing process has ended, a directly imaged printing forme of the type, which consists of materials, such as, for example, a ceramic, a glass or a metal, or has at least one surface layer consisting of one of these materials, can be erased within the printing machine in the way described there. This erasing and hydrophilic means is permanently installed in the printing assembly and is arranged on the circumference of the forme cylinder having a directly imageable printing forme. It has a cleaning device which can be thrown onto and off the printing forme. The cleaning device operates by means of a cleaning cloth or cleaning fleece which is pressed against the printing forme by a supply roller via a pressure roller and is subsequently wound up onto a winding roller. The pressure roller is likewise mounted rotatably, for example in an oscillating head. When a cleaning fluid or another agent, which serves either for erasing the printing image applied to the printing forme and for the removal of printing-ink residues or for hydrophilizing, that is to say conditioning the surface of the printing forme, is applied to said printing forme from nozzles which are located upstream of the cleaning device in the direction of rotation of the forme cylinder, this agent can be taken up, together with the dirt detached by it, by the cleaning cloth when the pressure cylinder presses the pressure roller against the printing forme and the cleaning cloth is moved past the printing forme. The nozzles are preferably angularly adjustable and spray the media either directly onto the printing forme or onto the cleaning cloth. The pressure roller is preferably rubber-coated. The cleaning cloth is wound from the supply roller onto the winding roller either in portions or continuously. The pressure with which the cleaning cloth is pressed against the printing forme is preferably also variably adjustable.
By contrast, EP 0 611 652 B1 shows a cleaning device for cleaning the surface of the rubber blanket of a rubber-blanket cylinder. It likewise comprises essentially a fresh-cloth roller and a dirty-cloth roller for receiving a cleaning cloth which is impregnated with washing fluid and is drawn off from the fresh-cloth roller to the dirty-cloth roller. In this case, the cleaning cloth is always held under tension stress by pressure means.
The cleaning device is designed, there, as a push-in unit system and, in the pushed-in state, is assigned to the cylindrical body produced in the form of a rubber-blanket cylinder. The cleaning device is brought into or out of contact with the rubber-blanket cylinder via a throw-on device. A washing-fluid supply is assigned to the cleaning device fixedly in relation to the machine. The fresh-cloth roller, the washing roller and the dirty-cloth roller are rotatably mounted in two side parts arranged parallel to one another. The washing roller has a shaft which possesses an elastic coating and which serves as a pressure element for pressing the cleaning cloth onto the cylindrical body and at the same time guiding the cleaning cloth. The side parts of the push-in unit system are connected to one another via a crossmember. The cleaning cloth is guided by the fresh-cloth roller at as large a looping angle as possible over the washing roller in the pulling direction of the dirty-cloth roller. The cleaning cloth is wetted via a washing fluid. Drive is imparted to the dirty-cloth roller via a shaft and gearwheel. The dirty-cloth rollers operated intermittently and pulls off the cleaning cloth from the fresh-cloth roller in the pulling direction via the washing roller, which brings the cleaning cloth into contact with the cylindrical body to be cleaned, and receives the cleaning cloth on a shaft.
The cleaning cloth running off from the stock roll on a clean-cloth spindle is guided on the outside around the pressure element which is arranged so as to be linearly movable and which consists of an elastic material.
During the change of cleaning cloth, hitherto the front end of the cloth web has had to be pulled through the washing device by hand and guided via the deflections on the outside around the pressure element to the dirty-cloth roll and secured to the latter.
The object of the present invention is to make it easier to change the cleaning cloth and to reduce the time taken up by this change and, moreover, to design an erasing and cleaning device in such a way that it can be used universally.
Since all the cleaning-cloth transport means, together with the cleaning cloth, are packaged in an independent cassette and a modular positioning unit can be arranged permanently in the printing machine, universal use of the cassette in the printing machine for any desired cylinder is possible, and it is merely necessary to provide a positioning unit. A particular advantage, as compared with the push-in unit system described in the introduction with regard to the prior art, is also to be seen in that the cleaning device no longer has to be exchanged completely, but, instead, only the independent cassette has to be taken out of the positioning unit, thus greatly simplifying the change, not simply in terms of time.
The device for erasing and cleaning cylindrical surfaces comprises a fresh-cloth roll, a dirty-cloth roll for receiving the spent cleaning cloth and a pressure element, in particular a pressure roller, which presses the cloth against a cylindrical surface. In a particularly advantageous way, a transport device is arranged on the path between the fresh-cloth roll and the pressure roller and an identically designed transport device is arranged on the path from the pressure roller to the dirty-cloth roll, these transport devices comprising devices 3xe2x80x2 and 3xe2x80x3 which are similar to transport belts and between which the cleaning cloth runs, on the one hand the devices 3xe2x80x3 being equipped with mechanical means which ensure a take-up of the cleaning cloth, and, on the other hand, the devices 3xe2x80x2 being controlled synchronously via drive devices. The elements 1-4 and 6 are, in turn, arranged in a cassette. A cassette is thus provided which ensures the synchronization of the cleaning cloth in a simple way, the cleaning and erasing device as a whole therefore being less susceptible to faults and requiring lower maintenance.
The advantageous arrangement of active transport devices for the cleaning cloth both in the region of the fresh-cloth roll and pressure roller and between the pressure roller and dirty-cloth roll ensures, at any moment, an equal feed and a uniform tension of the cloth between the three rollers, so that, for example, non-uniformity in transport due to the decrease in roll thickness on the fresh-cloth roll is compensated.
Moreover, the direction of the cloth can be reversed in a simple way without difficulty. Thus, for example, fresh-cloth roll and dirty-cloth roll need to be operated with slip merely via conventional take-up drives which wind up and unwind the cloth and ensure sufficient tension between the transport devices 3xe2x80x2 and 3xe2x80x3 according to the invention and the respective rollers.
The active transport device 3xe2x80x2 has, on its surface, gripping means which can engage into the fleece of the cleaning cloth and thus move it forwards. These gripping means may consist of fine hooklets, in a similar way to a touch-and-close fastening, but may also be other roughnesses, for example knobs or needles, or may consist of profiled rubber. The device 3xe2x80x3 similar to a transport belt forms a passive abutment for the active transport device 3xe2x80x2 and may consist, for example, of an elastomeric band. In a further embodiment, this band may also be provided with take-up means and be actively operated synchronously with the devices 3xe2x80x2 via a further drive.
By such gripping cloth transport being used, the mechanical properties of the cleaning cloth are relatively independent of the mechanical requirements of the cloth transport device. Furthermore, the transport travel is independent of the angular diameter of the fresh-cloth and dirty-cloth rolls, while the drive may take place both continuously and in steps.
Contact between the cylindrical surface, for example of a printing forme, and a cloth, is made via the pressure roller, for example an elastic rubber roller. In a preferred embodiment, this elastic rubber roller may likewise be driven synchronously.
By means of the cleaning device according to the invention, a cleaning cloth can be used both as a single piece or as a perforated band. The cylinder segment required (active cleaning surface) may be small and variable. Any desired cleaning-cloth rolls may be used in the application, since the mechanically gripping transport devices are independent of the physical and chemical nature of the cleaning cloth. As compared with known devices, there is no complicated control carried out, for example, via sensors. The control of the drives for devices 3xe2x80x2 and 3xe2x80x3 and, if appropriate, pressure roll 4 is restricted merely to the synchronous behavior which is directly predetermined.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.